FYI, a knacker is a very derogatory term for a traveler, a lot of them have settled down and have houses and don't life in caravans anymore.
however due to their lack of education a lot of them have a very poor chance of getting jobs and seem to be on the very low end of society.
The following example is recorded in Athlone but I could show you a 100 of examples I see on a daily basis.